In the past, vehicular damping systems have included springs, viscous dampers and torsion bar systems. The particular design parameters will be selected to suit the application requirements as defined by the systems' characteristic equations of motion.
Spring systems, for example, function to restore the system to its undisturbed position. Since they are elastic, they absorb and return energy without dissipating any.
By comparison, the energy input to viscous dampers is dissipated as heat which is lost to the environment and not returned as kinetic energy. Hence, the frictional dampers act to reduce the amplitude of chassis motion with time.
Torsion bars display mechanical characteristics similar to springs and, therefore, present similar problems in terms of defining an optimum construction for all displacements. Comparatively soft springs fail to absorb the more severe suspension shocks because their travel becomes excessive, yet they will effectively dampen high frequency vibrations. On the other hand, comparatively stiff springs do little to dampen high frequency, low amplitude oscillations, while effectively reducing the travel for severe shocks.
Typical viscous damping systems include a tight fitting displacement piston having an internal orifice and positioned within a liquid filled cylinder. Some net pressure is required in order to pass fluid through the internal orifice. This pressure, acting on the piston, tends to slow the axial motion of the piston within the cylinder. The faster the plunger is displaced, the larger the restraining force acting upon it, conversely, a slower motion will encounter substantially less resistance. Since inertia keeps a body from developing a velocity quickly, the main viscous restraining effect will be delayed until the higher velocities are achieved. More elaborate systems of this type include built-in corrective mechanisms which anticipate this delayed effect.
Another open cycle (no servo control) system of a more sophisticated design can be found within an aircraft's landing gear oleo strut system. Here the orifice size is made a function of the piston stroke. A tapered pin passes through the orifice as the gear is compressed. Through this construction, the frictional restraining force is caused to depend in a fixed manner, upon the instantaneous combination of velocity and displacement. Modifications of this type suspension system have included the incorporation of computer controlled servo devices which vary the orifice size in response to computer signals. Better anticipation and hence comfort should be possible with this "closed loop" type of system.
Viscous dampers also incur difficulties due to their typical bulk and location. To provide the most effective suspension control, a hydraulic cylinder is interposed between a vehicle frame and each wheel. In many applications, such construction is inordinately space consuming and difficult to maintain.
By way of illustration, one problem encountered in armored military vehicles, concerns cooling the viscous damper. As hydraulic fluid repeatedly flows through the orifice, it becomes warmer, whereupon its resistance to flow will diminish, hence its damping characteristics are caused to change. The small surface to volume relationship, size and location of the cylinder and associated devices make convective cooling difficult.
Accordingly, it is, therefore, a major object of this invention to provide a relatively light weight frictional damping system adapted for use with a vehicular suspension system.
It is a further object of this invention to provide a versatile vehicular suspension damping system which is capable of centralized electronic control of a plurality of individual dampers, each associated with an individual wheel.
It is yet another object of the present invention to provide a simple, inexpensive and reliable system for damping vehicular oscillations due to terrain irregularities.